It has been known that a thionucleoside in which an oxygen atom is replaced with a sulfur atom shows antiviral activity and/or antitumor activity.
For instance, it has been known that 1-(2-deoxy-2-fluoro-4-thio-β-D-arabinofuranosyl)cytosine (hereinafter referred to as “Compound A” at times) has excellent antitumor activity, and that this compound is useful as a tumor therapeutic agent (Patent Literature 1). As a method for producing Compound A, a method using 1,2:5,6-di-O-isopropylidene-α-D-allofuranose has been known, for example (Patent Literature 1). In addition, a method using 5-O-benzyl-2,3-O-isopropylidene-L-lyxono-1,4-lactone has also been known (Patent Literature 2).
Moreover, as a method for producing a sulfur-containing 5-membered ring compound, a method of allowing a γ-halogenoester to react with potassium thioacetate (Non Patent Literature 1), a method of allowing a γ-halogenoketone to react with sodium hydrogen sulfide (Non Patent Literature 2), etc. have been known.